Vandals have defaced a memorial to the victims of the July 7, 2005 London bombings, on the ninth anniversary of the attack that left 52 people dead.

The stainless steel columns in Hyde Park on Monday were daubed with messages referencing former prime minister Tony Blair, who took Britain into the US-led wars in Iraq and Afghanistan, as well as the four suicide bombers.

The slogans, including “Blair Lied Thousands Died”, “4 Innocent Muslims” and “J7 Truth”, were stencilled onto the 11.5-foot (3.5m) columns in red and black paint, according to video shot by a local television channel.

Police were called at about 3.30am and staff from the Royal Parks service swiftly moved to clean the pillars ahead of a memorial service planned later in the morning.

“We found it this morning. It has now been removed and the memorial can go ahead as planned. Obviously, we are very disappointed,” a spokeswoman for the Royal Parks said.

The Metropolitan Police said it had launched an investigation into the graffiti, which is being treated as criminal damage.

The memorial consists of 52 columns, one for each victim, grouped to reflect the four bombing sites – a packed bus and three London Underground subway trains.

The al-Qaeda-inspired attack, Britain’s first suicide bombing, was carried out by four British Islamists.